Severe trauma is usually accompanied by losses of body protein (nitrogen), even under conditions of normal food intake. Our study is concerned with the reduction of these losses and the speed of recovery, especially as this might pertain to the aged. It is proposed to use an animal model using rats and to compare the 9 to 12-month-old young adult rat with the 18 to 24-month-old rat. We intend to study differences in protein and amino acid needs of the old, as compared with the young adult rat. It is then planned to apply this information to a study of hind leg fracture and the nutritional input that might be made to lessen the protein loss immediately subsequent to infliction of the stress. It is contemplated to vary the amino acid patterns of the diet offered to the rats on the assumption that particular essential amino acid patterns may reduce the protein losses. Finally, it is planned to study the relationship of varying copper and zinc levels in the diet on the protein losses during hind leg fracture. In all cases comparisons between the adult and the old rat will be carried out since the problems of trauma are believed to be particularly severe complicating factors in old age.